Conventionally, fuel consumption of vehicles has been improved by reducing rolling resistance (i.e. improving rolling resistance) of tires. Further reduction in fuel consumption of vehicles has been more and more strongly required in recent years, and a rubber composition for producing a tread, which occupies a larger portion of a tire among various tire components, is required to be excellent in rolling resistance.
Known as a method of improving rolling resistance of a rubber composition is a method in which the amount of a reinforcing filler in the rubber composition is reduced. However, this method causes reduction in hardness of the rubber composition, which problematically results in deterioration in handling stability and wet skid performance of tires.
Known as a method for solving such problems is a method in which silica is used as a reinforcing filler. Since silica has low affinity for a rubber component, silica is usually used in combination with silane coupling agents such as sulfide silanes and mercapto silanes. Patent Document 1, for example, discloses a rubber composition containing bis(3-triethoxysilylpropyl)tetrasulfide.
However, the use of the sulfide silanes tends to increase viscosity upon processing thereof, and the use of the mercapto silanes tends to reduce scorch time. Thus, the conventional silane coupling agents are required to be improved because processability of the rubber composition tends to be deteriorated. In addition, the method using silica requires an improvement because abrasion resistance tends not to be sufficiently improved due to lower reinforcing properties of silica than those of other reinforcing fillers such as carbon black.    Patent Document 1: JP 2002-363346 A